Benefits and Drawbacks of Swift for macOS Development

Big source: https://medium.com/@mayurkore4/the-evolution-of-swift-a-journey-through-apples-game-changing-programming-language-ccaca14404d7

Swift is the default language for macOS app development, offering benefits in performance, safety, and developer productivity (compared to Objective-C), but also some trade-offs. This page documents some of them.

Performance

Benefits (performance)

There are entire books on Swift performance!

Swift is a compiled, native language, which means macOS apps written in Swift can achieve performance on par with or superior to those written in Objective-C or C. Swift builds on the proven LLVM compiler infrastructure to produce optimized machine code. Its lack of a garbage collector (using ARC instead) avoids GC pauses and latency spikes; memory is managed continuously and deterministically. Many low-level optimizations are built into the language: for instance, bounds-checking on arrays can be optimized out in safe contexts, and ARC overhead is often reduced by compiler optimizations that eliminate redundant retain/releases. Apple has reported impressive performance using Swift: for example, a high-scale Apple service rewritten in Swift saw a 40% performance increase compared to its former Java implementation. Swift’s emphasis on value semantics (structs) also helps performance by enabling compiler optimizations and avoiding heap allocations when not needed. TLRD: Swift can have C-like-ish speed with high-level convenience, and its performance has many optimizations, better concurrency (non-blocking async/await), and cool features like ownership control that let experts eliminate copies for efficiency.

Drawbacks (performance)

The primary performance cost in Swift comes from ARC. While ARC is generally efficient, it inserts retain/release calls that add overhead, especially in tight loops or performance-critical sections manipulating lots of class objects. In some cases, this overhead means Swift’s pure performance can lag a manual-memory-managed C++ implementation (which has no automated reference counting) or even Objective-C in certain scenarios where ObjC’s runtime optimizes trivial getters/setters better. However, Swift’s ARC is highly optimized, and upcoming (?) features (like Swift’s move-only types and ownership qualifiers) are specifically aimed at reducing ARC traffic when not needed. Another potential drawback is compile-time performance: Swift’s compiler is doing heavy lifting (type inference, optimization, safety checks), and in early days Swift was apparently known for slow compile times on large projects. This has improved with each version (for instance, Swift 4.2 significantly sped up compilation), but compile times can still be higher than for simpler languages. Build optimization and debugging of performance issues (especially related to ARC memory traffic) can require more expertise from developers (e.g., using Instruments to profile retains/releases). Finally, Swift’s emphasis on safety (bounds checks, overflow checks on integers by default, etc.) can incur minor runtime costs. AFAIK these checks can mostly be eliminated by the compiler when it can prove safety, but in hot code paths a developer might need to use unsafe constructs to get max performance, losing the safety net in those parts. In practice, for nearly all macOS app use-cases, Swift’s performance trade-offs are well-balanced from what I can tell (again, I’m not a developer), but in ultra-low-latency or systems programming scenarios, I’d assume you would have to carefully manage ARC or opt out of it with lower-level code.

Safety and reliability

Benefits (safety)

Safety is one of Swift’s strongest advantages. The language was designed to eliminate entire classes of crashes and bugs that were common in C/Objective-C. Swift’s type system and compiler enforce memory safety: objects cannot be used after they’re deallocated (ARC ensures objects stay alive while in use), array indices are checked (preventing buffer overflows), and variables must be initialized before use. Moreover, Swift’s use of optionals provides a systematic way to handle nil values… rather than crashing on a null pointer, the compiler forces you to safely unwrap optionals or provide default values, dramatically reducing runtime NULL reference errors.

The result is that many common vulnerabilities and crashes (null dereferences, buffer overruns, use-after-free, double frees) are either impossible or extremely unlikely in pure Swift code. Swift also incorporates type safety to avoid type mismatches and undefined behaviors (e.g., no arbitrary pointer casting without explicit unsafe code). With Swift 5.5+ introducing structured concurrency, the language also tackles thread safety: data races are largely avoided by design (for example, actor objects serialize access to their state), and Swift 6’s new data race checker can catch concurrent access issues at compile time. All these features lead to Swift apps that are less crash-prone and more secure. Apple observed that many of the serious security vulns in its platforms stem from memory-unsafe code (C/C++: what’s new here, lol), and using Swift can preempt these. Newer memory-safe languages like Swift “provide the first four memory safety properties - temporal, spatial, type, and initialization safety - by default,” (condense quote) which directly prevents the most widely exploited class of software vulnerabilities (memory corruption). In practice, from what I’ve read, macOS apps in Swift are far less likely to suffer from buffer overflow exploits or heap corruption errors that plagued apps in the past.

Drawbacks (safety)

It’s hard to call safety a drawback, but the strictness of Swift’s safety can have downsides in terms of learning curve and flexibility. Developers coming from more relaxed languages might find Swift’s insistence on unwrapping optionals or handling errors verbose or cumbersome. For example, the compiler will not let us ignore the possibility of nil or a thrown error without explicitly handling it; this leads to more code for checks, which some might consider boilerplate (though it’s there for good reason). In certain systems-level programming tasks, Swift’s safety can be an obstacle; you may need to drop into unsafe operations (with UnsafePointer or similar) to, say, interface with a C library or implement a highly optimized algorithm. Once you go into Unsafe territory, all safety bets are off (YOLO), and the onus is on you to avoid errors. Basically you’re in “C mode” within those parts of the code.

Another consideration is that Swift’s runtime safety checks (like array bounds checking) incur slight overhead. For the vast majority of apps this is negligible, but in critical code you might disable checks (using functions like unsafeBitCast or unchecked arithmetic) and thereby risk crashes if something goes wrong. Memory leaks are another issue not directly prevented by Swift’s safety model: a retain cycle will cause a leak (objects never freeing), which isn’t a memory corruption but can still crash an app if memory grows unbounded. Swift won’t automatically break those cycles; it’s on you to use weak references appropriately. Thus, a poorly structured Swift app could still exhaust memory over time. Lastly, Swift’s safety features are primarily geared toward preventing unintentional errors; they don’t automatically make an app immune to logical flaws or higher-level security issues (an SQL injection or improper encryption usage is just as possible in Swift as in any language). TLDR: there are few direct downsides to Swift’s safety. The trade-off is typically rigor for flexibility. Most people I know consider this a net positive, but it does require adapting to Swift’s way of thinking to fully leverage (and not fight against) the safety features.

Integration with macOS frameworks

Benefits (framework integration)

Swift was engineered to interoperate with Objective-C, which is the backbone of macOS’s Cocoa frameworks. This means Swift can directly use macOS frameworks like AppKit, Foundation, and newer Swift-only frameworks like SwiftUI with little friction.

Existing Objective-C APIs are imported into Swift in a natural way; for instance, Obj-C’s [NSArray addObject:] becomes Swift’s Array.append(_:). Swift code can subclass Objective-C classes or implement Obj-C protocols, and vice versa (you can subclass a Swift class in Obj-C if it’s marked appropriately). Apple ensured toll-free bridging for core types (Swift String <-> NSString, Array <-> NSArray, etc.), so many frameworks work with Swift value types out of the box. On macOS, this means you can leverage decades of Cocoa development (like NSView, NSWindow, etc.) while writing your app logic in Swift; you get the safety and conciseness of Swift with the abilies of the Cocoa frameworks. The introduction of SwiftUI in 2019 is a testament to integration: SwiftUI is a modern UI toolkit built in and for Swift, allowing native apps to be developed in a declarative Swift syntax. Swift also interoperates with lower-level C APIs commonly used in macOS development (like Core Graphics, POSIX calls, etc.); you can call C functions directly from Swift, and even work with C structures and pointers (with Swift’s UnsafePointer wrappers) fairly easily.

Drawbacks (framework integration)

While interoperability is strong, there are a few integration challenges to note.

Bridging gaps

Not every Objective-C API maps perfectly to Swift. Developers sometimes encounter APIs that use id/void* or certain C patterns that aren’t Swifty; calling these can require awkward development or use of unsafeBitCast. For instance, older Core Foundation APIs that return unmanaged objects require explicit memory handling in Swift (using Unmanaged<AnyObject>). Performance-wise, bridging between Swift and Obj-C can incur small overhead (e.g., converting a large NSArray to a Swift [Element] may copy the contents). Usually this cost is minor, but in tight loops it can matter.

Dynamic features

Some macOS frameworks rely on Obj-C runtime dynamism (like KVO - Key-Value Observing, or target-action patterns). Swift can use these, but the syntax and usage may be less straightforward. For example, KVO in Swift requires the observed property to be marked with @objc dynamic, and you use key paths instead of strings; it works, but it’s a bit different from pure Obj-C and can be less discoverable for newcomers. Another integration quirk is with macros and C preprocessor; Swift doesn’t use the C preprocessor, so certain macros (like common NS macros) are unavailable or have Swift alternatives. In some cases, there might not be a one-to-one Swift replacement, requiring a different approach.

Binary compatibility issues

Now that Swift’s ABI is stable on macOS, Apple can use Swift in system frameworks. However, this also means if you have a framework built with a newer Swift, you must ensure the deployment target OS has the Swift support (e.g., an app using SwiftUI’s latest features won’t run on older macOS versions that lack those Swift symbols). This is similar to any OS feature dependency, but it’s worth noting that Swift evolution is tied to OS releases for those frameworks. Early in Swift’s life (pre-ABI stability), one drawback was inability to distribute binary frameworks without bundling the Swift runtime, but that’s largely solved now. Mixing languages in a project is generally smooth, but it does add build complexity: you need a bridging header for Obj-C files to be seen by Swift, and sometimes subtle issues arise (like naming collisions or Swift name mangling vs Obj-C). Also, Swift’s stricter type checking can make some Cocoa patterns harder. For instance, variadic selectors or Obj-C methods that accept heterogeneous collections might need extra handling in Swift.

Lastly, for people familiar with Obj-C, the move to Swift means adapting to new patterns for things like memory management (you no longer explicitly retainCount or autorelease objects) and more value-type usage. This isn’t a drawback of Swift per se, but an integration consideration for teams transitioning large macOS apps from Obj-C to Swift - there’s a learning phase and potential refactoring of code architecture (e.g., embracing value types or protocol-oriented designs).